1. Field of the Invention
This invention relates to a charging generator installed in a vehicle, or to a generator/motor for a vehicle, and to a control device thereof, and particularly to constructions for preventing over-charging of a vehicle battery.
2. Background Art
To cope with increased electrical loads in vehicles and to raise fuel economy by reducing weight, increased output and reduced size and weight are being required in charging generators for vehicles, and one way of meeting these requirements is to supplement the magnetic field of the generator with a magnetizing force provided by permanent magnets and thereby reduce leakage flux between the magnetic poles and increase effective flux and increase output. However, in a generator with this kind of construction, even when no field current is passed and the generator operates with the magnetic flux of the permanent magnets only, at high speeds, and when the electrical load is small, it sometimes happens that electrical power exceeding the electrical load is generated, and the battery becomes over-charged and fails or an abnormal voltage is applied to electrical loads and causes them to fail.
In this connection, technologies have been proposed for, in a generator using permanent magnets for its magnetic field, reducing the power generated at high speeds and thereby preventing failure of a battery and electrical loads caused by over-voltage. One example of this is the technology disclosed in Patent Document 1: in the technology disclosed in this document, in a generator having a claw pole type rotor, permanent magnets magnetized in a direction such that they reduce leakage flux inserted between the magnetic poles of the rotor core constituting the field; a clutch is interposed between a pulley driving the rotor and the rotor shaft, and when the internal combustion engine goes above a predetermined speed the clutch outer idles and the clutch inner and the rotor maintain a predetermined speed; and the output voltage of the generator at this predetermined speed is approximately matched to the battery voltage.
And, in Patent Document 2, technology is disclosed wherein, in a generator having a field rotor constructed with permanent magnets, the output of the stator (armature) charges a battery by way of a three-phase full-wave rectifier; the neutral point of the three-phase winding of the armature is grounded via a switching device; this switching device is turned ON and OFF periodically in synchrony with the rotation to repeatedly short-circuit and re-circuit the armature coil and generate a flyback voltage; the battery is charged with this flyback voltage; and the specifications of the field magnets and the armature coil are made such that when there is no ON-OFF switching of the switching device the output voltage of the armature coil does not exceed the battery voltage even at maximum speed.
Further, in Patent Document 3, technology is disclosed wherein, in an alternator for a vehicle having permanent magnets magnetized in a direction such that they reduce leakage flux inserted between the magnetic poles of a claw pole type rotor, when a field current is not supplied to the field coil of the rotor, most of the flux of the permanent magnets is shorted by the armature core and very little flux is supplied to the armature from the magnetic pole faces, and on this basis the specifications of the permanent magnets are adjusted to a magnetizing force such that the generator output at maximum speed when the field current has been made zero is substantially equal to the normal load demand value of the vehicle and does not exceed this.
Patent Document 1:
JP-A-2000-92800 (Para. 4, FIGS. 1 and 2)
Patent Document 2:
JP-A-2002-95175 (Paras. 3 and 4, FIG. 1)
Patent Document 3:
Patent Number 2674556 (Paras. 2 and 3, FIGS. 1 to 4)
In the examples of related art described above, with the technology disclosed in Patent Document 1, because a clutch is provided on the generator, increased cost is unavoidable, and, around the predetermined speed at which the clutch goes OFF the clutch comes ON and goes OFF repeatedly so that there remains problem of durability. And, the technology disclosed in Patent Document 2 puts a limit on the output characteristic.
Also, in the technology disclosed in Patent Document 3, when after excitation by a field current is carried out the field current is brought to zero a residual magnetism remains in the field core, and even if the magnetizing force of the permanent magnets has been adjusted, the output at high speeds increases because of this residual magnetism. In particular, when this generator is used as a synchronous motor and made a charging generator cum starter motor, the excitation current becomes large, and when the claw pole type rotor core is manufactured by plastic deformation the residual magnetism also becomes large and output suppression at high speeds becomes difficult, and there remains a danger of the battery becoming over-charged.